A combustion control apparatus includes a memory circuit which generates an alarm signal and generates also a signal for stopping the combustion in the apparatus and which maintains its non-combustion state, when an abnormal condition such as abnormal heating, shortage of a medium (water) to be heated or ignition failure is sensed.
However, malfunction of such apparatus has occurred frequently due to the fact that this memory circuit is generally easily affected by noise, which can easily enter this memory circuit. This malfunction is objectionable as it may lead to an interruption of the combustion in the apparatus.
In the combustion control apparatus, noise is generated due to on-off operation of electromagnetic relays for various external output units driven by combustion control output signals from a combustion control circuit in the apparatus and also due to on-off operation of a fuel supply unit, a combustion blower and an ignition unit driven by the relays above described. Such noise is applied to the memory circuit through an input circuit and gives rise to a source of malfunction of the apparatus.